diff --git a/.github/sync-repo-settings.yaml b/.github/sync-repo-settings.yaml
index af19545c80..f6bda66b9f 100644
--- a/.github/sync-repo-settings.yaml
+++ b/.github/sync-repo-settings.yaml
@@ -22,7 +22,6 @@ branchProtectionRules:
     - 'Presubmit - Unit Tests Python 3.11'
     - 'Presubmit - Unit Tests Python 3.12'
     - 'Presubmit - Unit Tests Ray 2.9.3'
-    - 'Presubmit - Unit Tests LangChain (Python 3.8)'
     - 'Presubmit - Unit Tests LangChain (Python 3.9)'
     - 'Presubmit - Unit Tests LangChain (Python 3.10)'
     - 'Presubmit - Unit Tests LangChain (Python 3.11)'
\ No newline at end of file
diff --git a/.kokoro/presubmit/unit_langchain_py38.cfg b/.kokoro/presubmit/unit_langchain_py38.cfg
deleted file mode 100644
index ecfef00cdc..0000000000
--- a/.kokoro/presubmit/unit_langchain_py38.cfg
+++ /dev/null
@@ -1,13 +0,0 @@
-# Format: //devtools/kokoro/config/proto/build.proto
-
-# Run unit tests for LangChain on Python 3.8
-env_vars: {
-    key: "NOX_SESSION"
-    value: "unit_langchain-3.8"
-}
-
-# Run unit tests in parallel, splitting up by file
-env_vars: {
-    key: "PYTEST_ADDOPTS"
-    value: "-n=auto --dist=loadscope"
-}
diff --git a/noxfile.py b/noxfile.py
index 48ca9b0e30..282461dc21 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -52,6 +52,7 @@
 )
 
 UNIT_TEST_PYTHON_VERSIONS = ["3.8", "3.9", "3.10", "3.11", "3.12"]
+UNIT_TEST_LANGCHAIN_PYTHON_VERSIONS = ["3.9", "3.10", "3.11", "3.12"]
 UNIT_TEST_STANDARD_DEPENDENCIES = [
     "mock",
     "asyncmock",
@@ -275,7 +276,7 @@ def unit_ray(session, ray):
     )
 
 
-@nox.session(python=UNIT_TEST_PYTHON_VERSIONS)
+@nox.session(python=UNIT_TEST_LANGCHAIN_PYTHON_VERSIONS)
 def unit_langchain(session):
     # Install all test dependencies, then install this package in-place.
 
diff --git a/setup.py b/setup.py
index 21db80de42..173266ebf7 100644
--- a/setup.py
+++ b/setup.py
@@ -123,6 +123,7 @@
 
 genai_requires = (
     "pydantic < 3",
+    "typing_extensions",
     "docstring_parser < 1",
 )
 
@@ -143,7 +144,8 @@
     "google-cloud-trace < 2",
     "opentelemetry-sdk < 2",
     "opentelemetry-exporter-gcp-trace < 2",
-    "pydantic >= 2.6.3, < 2.10",
+    "pydantic >= 2.6.3, < 3",
+    "typing_extensions",
 ]
 
 evaluation_extra_require = [
diff --git a/testing/constraints-langchain.txt b/testing/constraints-langchain.txt
index 2be9f67361..14ba97ad53 100644
--- a/testing/constraints-langchain.txt
+++ b/testing/constraints-langchain.txt
@@ -1,4 +1,3 @@
 langchain
 langchain-core
-langchain-google-vertexai
-pydantic<2.10
\ No newline at end of file
+langchain-google-vertexai
\ No newline at end of file
diff --git a/vertexai/generative_models/_generative_models.py b/vertexai/generative_models/_generative_models.py
index 462861ca5b..cd845d6630 100644
--- a/vertexai/generative_models/_generative_models.py
+++ b/vertexai/generative_models/_generative_models.py
@@ -117,6 +117,51 @@
     ],
 ]
 
+try:
+    # For Pydantic to resolve the forward references inside these aliases.
+    from typing_extensions import TypeAliasType
+
+    PartsType = TypeAliasType(
+        "PartsType",
+        Union[
+            str,
+            "Image",
+            "Part",
+            List[Union[str, "Image", "Part"]],
+        ],
+    )
+    ContentsType = TypeAliasType(
+        "ContentsType",
+        Union[
+            List["Content"],
+            List[ContentDict],
+            str,
+            "Image",
+            "Part",
+            List[Union[str, "Image", "Part"]],
+        ],
+    )
+    GenerationConfigType = TypeAliasType(
+        "GenerationConfigType",
+        Union[
+            "GenerationConfig",
+            GenerationConfigDict,
+        ],
+    )
+    SafetySettingsType = TypeAliasType(
+        "SafetySettingsType",
+        Union[
+            List["SafetySetting"],
+            Dict[
+                gapic_content_types.HarmCategory,
+                gapic_content_types.SafetySetting.HarmBlockThreshold,
+            ],
+        ],
+    )
+except ImportError:
+    # Use existing definitions if typing_extensions is not available.
+    pass
+
 
 def _reconcile_model_name(model_name: str, project: str, location: str) -> str:
     """Returns a model name that's one of the following: